Changes in greening in the high Arctic: insights from a 30 year AVHRR max NDVI dataset for Svalbard

Abstract

Satellite-aided studies ofvegetation cover, biomass and productivity are becoming increasingly
\nimportant for monitoring the effects ofa changing climate on the biosphere. With their large spatial
\ncoverage and good temporal resolution, space-borne instruments are ideal to observe remote areas over
\nextended time periods. However, long time seriesdatasets with global coverage have in many cases too
\nlowspatial resolution for sparsely vegetated high latitude areas. Thisstudy has made use ofa newly
\ndeveloped 30 year 1 kmspatial resolution dataset from 1986 to 2015, provided bythe NOAAAVHRR
\nseries ofsatellites, in order to calculate the annual maximum NDVI over parts of Svalbard
\n(
\n78
\n°
\nN
\n)
\n.This
\nparameterisindicative ofvegetation productivity and has therefore enabled usto study long-term
\nchanges in greeningwithin the Inner Fjord Zone on Svalbard. In addition, local meteorological data are
\navailabletolinkmaximumNDVIvaluesto the temporalbehaviorofthe meangrowingseason
\n(
\nsummer
\n)
\ntemperature for the study area. Overthe 30 yearperiod, we
\nfi
\nnd positive trends in both maximum NDVI
\n(
\naverage increase of29%
\n)
\nand mean summer temperature
\n(
\n59%
\n)
\n, which were signi
\nfi
\ncantly positively
\ncorrelated with each other.Thissuggests a temporal greening trend mediated by summer warming.
\nHowever, as also recently reported for lower latitudes, the strength ofthe year-to-year correlation
\nbetween maximum NDVI and mean summer temperature decreased, suggestingthatthe response of
\nvegetationto summer warming has not remainedthe same overthe entire study period.